Self-adjusting pliers are described, for example, in U.S. Pat. No. 4,651,598, which is incorporated by reference herein in its entirety. Self-adjusting, or "auto-grip," pliers such as disclosed in this patent provides the capability of one-handed adjustment, wherein the pliers jaws automatically adjust to the size of a work piece in response to a user's manual closing action on the pliers' handles.
Many prior art hand tools, such as the pair of pliers disclosed in the 4,651,598 patent, are produced via forging operations, wherein the pliers' main body members are of essentially one-piece, forged steel construction. Usually, the tool begins as pieces of bar stock that are forged to obtain the basic shape of the pliers' body members. The roughly shaped pliers body members are then machined to get the final, desired tool shape. These multiple operations are inefficient, resulting in waste and added labor costs which, in turn, increase the cost of the finished tool. To partially compensate for the costs of the waste produced with forged construction, inexpensive materials, such as high-carbon steel, are typically used for fabricating tools such as pliers. This, however, may result in pliers, especially pliers jaws, that do not have the proper hardness characteristics required for many applications.
U.S. Pat. Nos. 4,662,252 and 5,351,584, incorporated herein by reference in their entirety, disclose self-adjusting pliers that operate in a similar manner. However, the main body members, including the pliers jaws, are constructed out of laminated sheet metal stampings, rather than one-piece, forged steel. While this may result in a cost and efficiency improvement over tools constructed via forging processes, the laminated construction does not provide pliers jaws having the hardness characteristics desired for many applications.
A pliers jaw assembled entirely of laminated sheet metal stampings rather than a single forged piece must be held together by fasteners such as rivets. Shear stresses placed on the jaw during use of the pliers tend to concentrate in the fasteners, sometimes causing them to fail. This difficulty would be somewhat intensified if the jaws of the pliers were made of stronger material, as suggested above, because the fasteners holding the jaw to the handle would become the weak point in the tool. Thus a complete solution requires that the handle carry the shear stresses from the jaw directly rather than through intervening fasteners or other small cross-section components.
A further difficulty sometimes encountered with some self-adjusting pliers of the type described above is that the locking mechanism of the jaw can sometimes engage when the tool is in its full open position, allowing the tool to stick or jam in that position.
Thus, a need exists for a pair of self-adjusting pliers that addresses the shortcomings of the prior art.